Genomic Investigation of Population Structure in a Secretive, Semi‐Fossorial Snake (Colubridae: Tropidoclonion lineatum ) Across the Great Plains

ABSTRACT With advances in genomic technologies, it has become increasingly feasible to generate large numbers of loci to address population genetic and phylogeographic questions. Nevertheless, many widespread and relatively abundant species remain unsampled using molecular approaches. The lined snake ( Tropidoclonion lineatum ), a semi‐fossorial snake distributed across the Great Plains, is one such example. Despite the historical recognition of multiple subspecies based on noted variation in morphological characters, no formal molecular investigation of population structure has been conducted to date due to a paucity of vouchered genetic samples. Here, we present the first genomic assessment of range‐wide population structure in T. lineatum using genome‐wide single‐nucleotide polymorphisms (SNPs) generated via triple‐enzyme restriction site‐associated DNA (3RAD) sequencing. Our results indicate largely continuous gene flow across the Great Plains, questioning the validity of the recognized subspecies. In contrast, populations at the northern range edge in South Dakota exhibit relative genetic homogeneity and modest differentiation from more southern populations, potentially reflecting recent isolation or increased genetic drift in peripheral habitats. Given the species' endangered status in South Dakota, these findings highlight the conservation importance of range‐edge populations while underscoring the need for denser, range‐wide sampling—particularly in putatively disjunct regions—to fully characterize genetic diversity in T. lineatum .